Blends of ethylene vinyl alcohol copolymer and amorphous polyamide, and multilayer containers made therefrom

ABSTRACT

Blends of a major portion of ethylene vinyl alcohol copolymer (EVOH) and a minor portion of an amorphous polyamide and preferably also a semicrystalline nylon are disclosed. These blends may be formed into films or multilayer structures, which can be thermoformed into containers or other articles. The presence of the minor portion of amorphous polyamide permits thermoforming of the EVOH at lower temperatures without the formation of defects.

This is a division of U.S. application Ser. No. 07/301,473, filed Jan.26, 1989, U.S. Pat. No. 4,990,562, which in turn is acontinuation-in-part of U.S. application Ser. No. 07/088,261, filed Aug.24, 1987, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to blends of ethylene vinyl alcohol copolymerwith a minor amount of amorphous polyamide component and their use as abarrier layer in thermoformed multilayer containers and otherapplications.

Blends of ethylene vinyl alcohol polymers with polyamides in general areknown, and have been used in packaging applications as barriers toinhibit the passage of atmospheric oxygen or other gases.

Japanese patent application 53-49050 discloses a blend of EVOH with 5 to40 weight percent polyamide. The polyamides include a copolymer ofhexamethylene diamine with isophthalic and terephthalic acids, in moleratios of 100/0 to 50/50. The blend is formed into a film, which is saidto possess excellent gas barrier properties.

U.S. Pat. No. 3,726,034, Bottenbruch et al., discloses mixtures of70-99% polyamide and up to 30% of a hydroxyl containing polyolefin. Thepolyamides "consist of linear unbranched polymer chains containing noadditional functional groups." Exemplified are blends of nylon 6 andEVOH.

U.S. Pat. No. 4,079,850, Suzuki et al., discloses a multilayer blowmolded container, which contains a layer which may be EVOH, polyamide,or various blends, providing gas barrier properties. The polyamideswhich are mentioned are nylon 6, nylon 66, and nylon 12.

U.S. Pat. No. 4,427,825, Degrassi et al., discloses a composition ofmatter useful for making films, of polyamide and 1-65% EVOH. Nylons withmelting points greater than 175° C. are preferred, such as nylon 11 ornylon 12.

U.S. Pat. No. 4,500,677, Maruhashi et al., discloses a resin compositioncomprising a mixture of two EVOH resins and a polyamide resin. The ratioof the EVOH resins to the nylon resin can be between 95:5 and 5:95.Nylon 6, nylon 6,6 and other polyamides having "linear alkylenegroup[s]" are specifically mentioned.

Ethylene vinyl alcohol copolymer (EVOH) is commonly used in the form ofa thin layer together with thicker layers of less expensive structuralmaterials, for example, polypropylene or polyethylene terephthalate, inorder to form a structure which is resistant to the passage ofatmospheric oxygen or other gasses. In order to make containers ororiented films of such multi-layer structures a solid phasethermoforming process is often used. However, EVOH cannot be formed atthe relatively lower temperatures required for the thermoforming of manycommon structural materials without rupturing the EVOH layer, resultingin a loss of overall barrier performance. The present invention providesa modified EVOH composition which may be used in thermoformed multilayerstructures to avoid the above mentioned problems, and withoutsubstantially sacrificing the excellent gas barrier properties of EVOH.It may also be used in other applications where stretching is requiredduring the processing of the article, such as in shrink films.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a blend consisting essentially of about50 to about 95 percent by weight of an ethylene vinyl alcohol copolymerhaving a copolymerized ethylene content of about 20 to about 60 molepercent and a degree of saponification of at least about 90 %, and about5 to about 50 percent by weight of a polyamide blend consistingessentially of about 30 to about 90 percent by weight of at least oneamorphous polyamide and about 10 to about 70 percent by weight of atleast one semicrystalline polyamide which is miscible with the ethylenevinyl alcohol copolymer. The present invention also provides filmsprepared of such blends, multiple layer structures including a layer ofsuch blend, and formed structures prepared by stretching orthermoforming such multiple layer structures. In addition, the presentinvention provides a formed structure prepared by thermoforming amultiple layer structure wherein at least one of the layers is a blendconsisting essentially of about 50 to about 95 percent by weight of anethylene vinyl alcohol copolymer having a copolymerized ethylene contentof about 20 to about 60 mole percent and a degree of saponification ofat least about 90%, and about 5 to about 50 percent by weight of anamorphous polyamide and at least one layer of a structural polymer. Theinvention also includes oriented multilayer shrink films which includeat least one layer of such blends.

DETAILED DESCRIPTION OF THE INVENTION

Materials and structures with barrier properties are important in manyapplications. Of particular interest are packaging materials which arebarriers to the penetration of gases, such as oxygen, carbon dioxide,and various aromas.

In many packaging applications EVOH resins are used as relatively thincomponents of multilayer structures or containers. Usually the majorparts of the structures are made of less expensive "structural"materials, bound to the EVOH layer by adhesive layers. The fabricationprocess in converting multilayer structures into final products ofteninvolves a mechanical deformation operation, such as orientation,thermoforming, or stretching in general, depending on the final form ofthe desired structure. However, EVOH generally exhibits very poordrawability, that is, the ability to be stretched or deformed uniformlyat a temperature below its melting point. Quite often the stretching ordeformation operation induces cracks, discontinuity or thinning("neckdown") in the EVOH layer. As a result stretched or deformedmultilayer structures which include a layer of EVOH resin often exhibitinferior barrier properties.

For the purposes of this invention, a deformation process includes anyprocess for forming a shaped article (e.g., a film or a container) which(a) is distinct from the initial melt processing step and (b) which isperformed at a temperature which is elevated above room temperature butlower than the melting point of the polymeric structural material.Casting of a film would not be a deformation process according to thisdefinition because it is a melt processing step; vacuum-forming a filmto prepare a container would be a deformation process. Making a film bya blown tubular process may or may not be a deformation process,depending on the temperature of the tubing or bubble at the locationwhere blowing occurs. Examples of deformation processes includethermoforming (but excluding melt phase thermoforming), vacuum-forming,solid phase pressure forming, co-injection blow molding, co-injectionstretch blow molding, tube extrusion followed by stretching, scraplessforming, forging, and tubular or flat sheet oriented film processes.Examples of articles that can be prepared using deformation processesare films and containers such as bottles, jars, cans, bowls, trays,dishes, pouches, oriented films, and shrink films. Deformation ofpolymeric materials is not only a way to attain such final shapedarticles, but may also be a means to enhance barrier properties,mechanical properties, or even optical properties.

The temperature of the deformation step is usually determined by the"forming temperature" of the structural material, that is, thetemperature at which it can be deformed. The forming temperature of apolymer is not readily related to any material properties of thepolymer, except that it is normally higher than the T_(g) of thepolymer. In addition, this temperature is affected by the magnitude andrate of deformation of the particular process employed. The formingtemperature of a given material for a given process can be readilydetermined by a person skilled in the art with a minimum ofexperimentation. Many structural materials have a lower formingtemperature than that of EVOH, and it may be desirable for many reasonsto conduct a molding operation at as low a temperature as possible.Furthermore, it may be desirable to reach an extent of deformation ashigh as possible. Thus the temperatures used for the deformation of suchmultilayer structures may be so low or the extent of deformation may beso high that the drawability of the EVOH layer is exceeded. As aconsequence the desired deformed articles cannot be made without tearingor rupturing of the EVOH layer. The resulting discontinuities in theEVOH layer result in inferior oxygen barrier performance of theresulting article. An object of this invention is to provide a modifiedEVOH composition which may be used in deformed multilayer structures toavoid the above mentioned problems, and without substantiallysacrificing the excellent gas barrier properties of EVOH. This modifiedcomposition is a blend of EVOH with an amorphous polyamide and asemicrystalline polyamide.

The first component of the composition of the present invention is anethylene vinyl alcohol copolymer. The EVOH resins useful in thisinvention include resins having a copolymerized ethylene content ofabout 20 to about 60 mole %, especially about 25 to about 50 mole %.Copolymers of lower than about 15 to 20 mole % ethylene tend to bedifficult to extrude while those above about 60 or 65 mole % ethylenehave reduced oxygen barrier performance. These polymers will have asaponification degree of at least about 90%, especially at least about95%. A degree of saponification of less than about 90% results ininferior oxygen barrier properties. The ethylene vinyl alcohol copolymermay include as an optional comonomer other olefins such as propylene,butene-1, pentene-1, or 4-methylpentene-1 in such an amount as to notchange the inherent properties of the copolymer, that is, usually in anamount of up to about 5 mole % based on the total copolymer. The meltingpoints of these ethylene vinyl alcohol polymers are generally betweenabout 160 and 190° C.

Ethylene vinyl alcohol polymers are normally prepared bycopolymerization of ethylene with vinyl acetate, followed by hydrolysisof the vinyl acetate component to give the vinyl alcohol group. Thisprocess is well known in the art.

The second component of the present invention is a polyamide component.The polyamide component comprises about 5 to about 50 percent by weightof the total composition of EVOH plus polyamide, preferably about 10 toabout 35 percent, and most preferably about 15 to about 30 percent. Thepolyamide component is a blend of amorphous polyamide withsemicrystalline polyamide. In particular, blends of at least oneamorphous polyamide with 10 to 70 percent by weight of at least onesemicrystalline polyamide are suitable, and blends in which theamorphous polyamide comprise about 60 to about 80 percent by weight ofthe polyamide component are preferred.

The term "amorphous polyamide" is well known to those skilled in theart. "Amorphous polyamide," as used herein, refers to those polyamideswhich are lacking in crystallinity as shown by the lack of an. endothermcrystalline melting peak in a Differential Scanning Calorimeter ("DSC")measurement (ASTM D-3417), 10° C./minute.

Examples of the amorphous polyamides that can be used include thoseamorphous polymers prepared from the following diamines:hexamethylenediamine, 2-methylpentamethylenediamine,2,2,4-trimethylhexamethylenediamine,2,4,4-trimethylhexamethylenediamine, bis(4-aminocyclohexyl)methane,2,2-bis(4-aminocyclohexyl)isopropylidine, 1,4-diaminocyclohexane,1,3-diaminocyclohexane, meta-xylylenediamine, 1,5-diaminopentane,1,4-diaminobutane, 1,3-diaminopropane, 2-ethyldiaminobutane,1,4-diaminomethylcyclohexane, p-xylylenediamine, m-phenylenediamine,p-phenylenediamine, and alkyl substituted m-phenylenediamine andp-phenylenediamine.

Examples of polyamides that can be used include those amorphous polymersprepared from the following dicarboxylic acids: isophthalic acid,terephthalic acid, alkyl substituted iso- and terephthalic acid, adipicacid, sebacic acid, butane dicarboxylic acid, and the like.

Polyamides prepared from aliphatic diamines with aliphatic diacids arethe traditional semicrystalline nylons (also referred to as crystallinenylons) and are not amorphous polyamides. Polyamides prepared fromaromatic diamines and aromatic diacids are also known. However, certainof these all-aromatic polyamides are known to be intractable underordinary melt processing conditions, and thus are not normally suitable.Thus the preferred amorphous polyamides are those in which either thediamine or the diacid moiety is aromatic, and the other moiety isaliphatic. The aliphatic groups of these polyamides preferably contain4-8 carbon atoms in a chain or an aliphatic cyclic ring system having upto 15 carbon atoms. The aromatic groups of the polyamides preferablyhave mono or bicyclic aromatic rings which may contain aliphaticsubstituents of up to about 6 carbon atoms.

However, not all of these aromatic/aliphatic combinations willnecessarily provide suitable amorphous polyamides. For example,specifically metaxylylenediamine adipamide is not generally suitable forthis invention. This polymer readily crystallizes under heatingconditions typical for thermoforming operations, and also crystallizesupon orienting. This illustrates the fact that it is important todetermine that a particular polyamide is amorphous, and not to relysolely on the chemical structure of the polymer. This determination caneasily be made by DSC.

Specific examples of amorphous polyamides which are suitable for thisinvention include: hexamethylenediamine isophthalamide,hexamethylenediamine isophthalamide/terephthalamide terpolymer, havingiso/terephthalic moiety ratios of 100/0 to 60/40, mixtures of of 2,2,4-and 2,4,4-trimethylhexamethylenediamine terephthalamide, copolymers ofhexamethylene diamine and 2-methylpentamethylenediame with iso- orterephthalic acids, or mixtures of these acids. Polyamides based onhexamethylenediamine iso/terephthalamide containing high levels ofterephthalic acid moiety may also be useful provided a second diaminesuch as 2-methyldiaminopentane is incorporated to produce a processibleamorphous polymer.

The above amorphous polyamides may contain as comonomers minor amountsof lactam species such as caprolactam or lauryl lactam, even thoughpolymers based on these monomers alone are not amorphous. The importantfeature is that the polyamide as a whole must be amorphous. Thus smallamounts of these comonomers may be incorporated as long as they do notimpart crystallinity to the polyamide. In addition, up to about 10weight % of a liquid or solid plasticizer such as glycerol, sorbitol, ortoluenesulfonamide ("Santicizer 8" from Monsanto) may be included withthe amorphous polyamide.

For most applications the T_(g) of the amorphous polyamide (as measuredin the dry state, i.e., containing about 0.12 weight % moisture or less)should be in the range of about 80° C. to about 160° C., and preferablyabout 80° C. to about 130.C. Certain unblended amorphous polyamides, asdescribed above, have T_(g) s of around 125° C. when dry. The lowerlimit on T_(g) is not clearly demarked; 80° C. is an approximate lowerlimit. The upper limit on the T_(g) is likewise not clearly demarked.But amorphous polyamides with T_(g) above about 160° C. are not readilythermoformable when used as a barrier layer. Thus all-aromaticpolyamides, having aromatic groups in both acid and amine moieties, tendto have a T_(g) which is too high to permit thermoforming, and are thusnormally unsuitable for the purposes of this invention.

The polyamide component also includes at least one semicrystallinepolyamide. This term refers to the traditional semicrystalline nylons,which are generally prepared from lactams or amino acids, such as nylon6 or nylon 11, or from condensation of diamines such as hexamethylenediamine with dibasic acids, such as succinic, adipic, or sebacic acids.Copolymers and terpolymers of these polyamides are also included, suchas copolymers of hexamethylenediamine/adipic acid with caprolactam(nylon 6,66). Blends of two or more crystalline polyamides can also beused. The polyamides of the present invention, both semicrystalline andamorphous, are prepared by condensation polymerization, which is wellknown to those skilled in the art.

However, not all semicrystalline nylons are necessarily suitable for thepresent invention. The suitable nylons are those which are miscible withthe EVOH component, as evidenced by the presence of a single glasstransition temperature or a depressed melting point as measured by DSC.Examples of suitable semicrystalline nylons include nylon 6, nylon 66,nylon 6,66, and copolymers of nylon 6 and 12.

The blends of the present invention comprise about 50 to about 95percent by weight EVOH and about 5 to about 50 percent by weight of apolyamide blend consisting essentially of about 30 to about 90 percentby weight of at least one amorphous polyamide and about 10 to about 70percent by weight of at least one semicrystalline polyamide as describedabove. When less than about 5% of the polyamide blend is used, theimprovements in formability imparted by the invention are not fullyrealized. When more than about 50% of the polyamide blend is used theoxygen barrier properties of the blend are degraded. When the polyamideblend is more than about 70% semicrystalline polyamide the oxygenbarrier properties and processability are reduced. Preferably suchblends will contain about 75 to about 85 weight % EVOH and about 25 toabout 15% weight percent polyamide blend component. Of course, smallamounts of other material such as other polymers, processing aids,antioxidants, fillers, pigments, etc. may be included in the blendwithout destroying the essence of this invention.

The blends of the present invention may be prepared by blendingtechniques well known in the art, including the use of single or twinscrew melt processors or extruders. Blending is performed attemperatures sufficiently high to form a uniform melt of the componentsto be blended, typically about 200° to about 225° C., above the meltingpoints of the two components. The blends of the present invention may beprepared by blending EVOH and a preblended mixture of amorphouspolyamide and semicrystalline polyamide. Alternatively, they may beprepared by blending the three components simultaneously. The formerprocedure is preferred when the semicrystalline polyamide has a highmelting point, i.e., higher than about 225° C.

The blends of the present invention may be formed into a film, which maybe done by typical equipment such as extrusion casting or blown film ifdesired, by known techniques.

In addition, multiple layer structures which . contain one or morelayers of the blend of the present invention may be prepared. Thesestructures may be incorporated into containers, which take advantage ofthe oxygen barrier properties of the blend of the present invention. Inmaking multilayer containers, a structural layer will often be used, toprovide structural support for the blend layer. The materials used forthe structural layers may be made, for example, from any of a variety ofstructural polymers. Examples of such structural polymers includepolyolefins such as polybutylene, polypropylene (either homopolymers orcopolymers with ethylene), polyethylene homopolymer or co- orterpolymers of ethylene with other monomers such as vinyl acetate,carboxylic acids, such as acrylic acid, or methacrylic acid (with orwithout neutralization to form ionomers), polyethylene terephthalate orits copolymers, and polymers based on vinyl chloride or styrene, and thelike.

The various layers of such multiple layer structures may be heldtogether by any of a variety of adhesive resins. In general, suchadhesive resins are thermoplastic polymers having carbonyl groupsderived from functional groups of free carboxylic acids, carboxylic acidsalts, carboxylic acid esters, carboxylic acid amides, carboxyicanhydrides, carbonic acid esters, urethanes, ureas or the like. In thesethermoplastic polymers, the carbonyl group concentration may be changedin a broad range, but in general, it is preferred to use a thermoplasticpolymer containing carbonyl groups at a concentration of 10 to 1400millimoles per 100 g of the polymer. Suitable adhesive resins includepolyolefins modified with at least one ethylenically unsaturated monomerselected from unsaturated carboxylic acids and anhydrides, esters andamides thereof, especially polypropylene, high density polyethylene, lowdensity polyethylene and ethylene-vinyl acetate copolymers modified withat least one member selected from acrylic acid, methacrylic acid,crotonic acid, fumaric acid, itaconic acid, maleic anhydride, itaconicanhydride, citraconic anhydride, ethyl acrylate, methyl methacrylate,ethyl maleate, 2-ethylhexyl acrylate, acrylamide, methacrylamide, fattyacid amides, and imides of the acids described above. The adhesive canalso be prepared from an ethylene polymer and a second polymer graftedwith maleic anhydride, as disclosed in U.S. Pat. No. 4,230,830, thedisclosure of which is incorporated herein by reference. In addition, asthe adhesive resin, there can be used ethylene-acrylate copolymers,ionomers, polyalkylene oxide-polyester block copolymers, carboxymethylcellulose derivatives, and blends of these polymers with polyolefins.

It has been discovered that the blends of this invention can be used tomake films and multiple layer structures which not only have excellentoxygen barrier properties, but also exhibit superior deformationcharacteristics. These structures can be deformed, stretched intobiaxially oriented film, or thermoformed into shaped containers withoutoccurrence of breaks or discontinuities in the EVOH blend layer, incontrast to the behavior of multilayer structures involving either EVOHby itself, or EVOH blended with crystalline polyamides. Thesestructures, furthermore, can achieve a high degree of deformation,orientation, thermoforming, or stretching in any form, in a broadtemperature range, in contrast to the behavior of either EVOH alone,EVOH blended with crystalline polyamide, or even EVOH blended withamorphous polyamide.

For certain applications, however, blends comprising about 50 to about95 (preferably about 70 to about 90) weight % EVOH, described above, andabout 50 to about 5 (preferably about 30 to about 10) weight % ofamorphous polyamide may be satisfactorily used, without additionalsemicrystalline polyamide. Such blends are useful in preparation ofthermoformed or stretch blow molded articles from a multilayer laminatein which at least one layer is such a blend. When less than about 5weight % of the amorphous polyamide is used, the thermoformability ofthe blend is not significantly improved. When more than about 50% of theamorphous polyamide is used the oxygen barrier properties of the blendare degraded. Most preferably such blends will contain about 75 to about85 weight % EVOH and about 25 to about 15% weight percent amorphouspolyamide component. Of course, small amounts of other material such asother polymers, processing aids, antioxidants, fillers, pigments, etc.may be included in the blend without destroying the essence of thisinvention.

The thermoforming or stretch blow molding operations for which such twocomponent blends are useful are those deforming operations, generallydescribed above, which further require that the blend be deformed inthree dimensions more or less simultaneously. The use of the amorphouspolyamide, even without the semicrystalline nylon, provides significantimprovements in such thermoformability in comparison with the resultsobtained when EVOH is used alone or as a blend with a semicrystallinenylon. For such thermoforming operations a comparatively thickmultilayer laminated sheet or preform is normally used, having a totalthickness preferably from about 0.5 to about 3.5 mm, preferably 0.5 toabout 3.0 mm, and most preferably about 1.0 to about 2.5 mm. This sheetwill preferably comprise at least one layer of the two component blend,typically about 10% of the total thickness, e.g. 0.05 to 0.35 mm thick,and at least one, and preferably two, structural layers as describedabove, about 0.25 to about 1.2 mm, and preferably about 0.5 to about 1.0mm, thick. Optional adhesive layers, as described above, may also beprovided. By the thermoforming process the sheet is converted into athree dimensional product of reduced thickness, typically about 0.15 mmto about 1.0 mm thick, preferably about 0.25 to about 0.75 mm thick.

While not wishing to be bound by any particular theory, it is believedthat the improvements of the present invention can be understood byconsidering the microscopic structure of blend of EVOH with polyamides.Electron microscopy shows that blends of amorphous polyamides with EVOHform two-phase systems. Electron microscopic examination of the corelayer of a structure prepared from a blend of EVOH with an amorphouspolyamide, Example 4 below, shows a distinctly two-phase structure, withparticle size of the amorphous polyamide inclusions in the 0.4 to 2micrometer range. After the thermoforming step, electron microscopyshows that the inclusions are deformed into thin lamellae, which arebelieved to reinforce the EVOH matrix. In contrast, electron microscopyof the core layer of a structure incorporating a blend of EVOH withnylon 612, semicrystalline, Comparative Example C6, below, beforethermoforming shows a similar two-phase structure. But afterthermoforming, the polyamide inclusions do not show significantdeformation. Thus it appears that the amorphous polyamides included inthe matrix can flow at temperatures lower than those which would berequired for deformation of crystalline polyamides. Yet another behavioris observed upon microscopic examination of the core layer ofcomparative example C4, below. This blend of EVOH with nylon 6 wascompatible and formed essentially a single phase structure with nosignificant visible domains of polyamide either before or afterthermoforming. When semicrystalline nylon is added to blends of EVOH andamorphous polyamide, however, it is believed that the semicrystallinenylon serves as a partially compatibilizing component.

EXAMPLES Example 1 and Comparative Examples C1-C3 Preparation of Blends

An EVOH polymer, containing 30 mole % ethylene and having a melt flowindex of 3, as measured at 210° C. with 2160 g weight (ASTM D-1238), wasmelt blended with one of a variety of polyamides, as indicated in TableI. For Example 1, an amorphous polyamide was used, the condensationpolymer of hexamethylenediamine (96.5 mole %),4,4-bis(aminocyclohexyl)methane (3.5 mole %) and a 70/30 mixture ofisophthalic and terephthalic acids. This polyamide is designated inTable I as "APA1." This polyamide was shown to be amorphous by the lackof any melting endotherm peak on DSC heating curves (ASTM D-3417). As acomparative example, (Cl) EVOH was blended with nylon 6,12, or wasevaluated without blending (C2 and C3). The weight ratios of the EVOHand the polyamides in each blend are indicated in Table I. Blending wasaccomplished on a twin-screw melt processor (extruder), 30 mm diameter,working at 50 rpm. The melt temperature was between 210° and 220° C. Thepolymer blend was extruded into a strand, cooled by air, and cut intopellets approximately 2 to 3 mm in diameter.

Physical Properties of Films

Films, 0.01 to 0.02 mm thick, were cast from the above blends, and forcomparison, from unblended EVOH resins, as indicated in Table I. Theoxygen permeabilities of these film samples were measured according toASTM D-3985. The results show that the oxygen barrier properties of theblend of EVOH with the amorphous polyamide are comparable to those ofunblended EVOH.

Preparation of Multilayer Structures

Next, samples of the blends used in the above examples, as well as theunblended EVOH resins, were coextruded into 1.5 mm multilayer sheetsamples. Three single screw extruders, a combining adapter, and a 35 cmwide single manifold sheeting die were used. The two surface layers,polypropylene homopolymers with a melt flow index of 4 (ASTM D-1238Condition L) and each 0.6 to 0.7 mm thick, were extruded on a 38 mmsingle screw extruder, L/D=24, turning at 75 rpm, at a melt temperatureof 233 C. Two adhesive layers, 0.02 to 0.04 mm thick, a blend of maleicanhydride grafted ethylene propylene copolymer in an ethylene vinylacetate copolymer matrix, were extruded on a 32 mm single screwextruder, L/D=24, turning at 6 rpm, at a melt temperature of 220° C. Thesample core layers (blends or EVOH) 0.1 mm thick, were extruded on a 25mm single screw extruder, L/D=24, equipped with a grooved feed section,turning at 10 rpm, with a melt temperature of 215° C. The casting rollswere cooled with water having a temperature of 95° C. The casting speedwas 0.6 m/min.

Thermoforming of Multilayer Structures

Subsequently, the cast multilayer sheets were thermoformed by solidstate pressure forming on an Illig™ RDM-37/10 continuous roll fedthermoformer into cylindrical, can shaped containers, 67 mm diameter and102 mm deep. The sheet samples were heated by ceramic heaters operatingat 320° C. to 380° C. The sheet samples attained the temperaturesindicated in Table II. Forming was accomplished by using plug assist,air pressure of 480 kPa, and molding rates of 10 to 12 cycles/min.

The formed containers made with the EVOH as the barrier layer exhibitedgrooves on their side walls running parallel to the axis of thecontainers. Microscopic examination of the cross section of thecontainer sidewalls cut perpendicular to the axis revealed numerousdiscontinuities of the EVOH core. It is believed that thesediscontinuities are the result of exceeding the formability limits ofthese EVOH resins during the thermoforming operation. Containers madewith blends of EVOH with the aliphatic, crystalline nylons also hadsimilar grooves. In contrast, the containers made using the blend ofEVOH with the amorphous polyamide did not exhibit grooves.

To quantify these findings, counts were made of the core interruptions(grooves or breaks) and core neck-downs (thinning of the core layerwithout actual discontinuity) per 25 mm wall section. The results aregiven in Table II. The thermoformed structure prepared using the blendof the present invention was greatly superior to the comparativeexamples in terms of number of breaks or neckdowns. Such discontinuitiesin the barrier layer of the container will necessarily result in loss ofbarrier performance.

                  TABLE I                                                         ______________________________________                                                                     THICKNESS                                        EXAMPLE  POLYAMIDE   (%)     (mm)      OPV.sup.1                              ______________________________________                                        1        APAI        10      0.011     0.0023                                 C1       nylon 612   10      0.018     0.0054                                 C2       none         0      0.018     0.0031                                 C3       none         0      0.021     0.0023                                 ______________________________________                                         .sup.1 cc-mm/m.sup.2 -day-atm at 30° C., 0% relative humidity     

                  TABLE II                                                        ______________________________________                                        THERMOFORMED COEXTRUDED SHEET                                                          TEMP             BREAKS/ NECKDOWNS/                                  EXAMPLE  (°C.)                                                                          DRAW.sup.1                                                                             25 mm   25 mm                                       ______________________________________                                        1        163     6.9      0        6                                          C1       163     6.7      6       34                                          C2       162     6.5      8       34                                          C3       164     6.9      25      11                                          ______________________________________                                         .sup.1 Ratio of initial to final film thickness                          

Examples 2-6 and Comparative Examples C4-C9 Preparation of Blends

For these blends, the same ethylene vinyl alcohol copolymer was used asin Example 1. This EVOH was blended with a condensation polymer ofhexamethylenediamine with a 70/30 mixture of isophthalic andterephthalic acids, which is designated in Table III as "APA2." Thispolyamide was shown to be amorphous by the lack of any melting endothermpeak on DSC heating curves (ASTM D-3417). For comparative examplesC4-C6, the EVOH was blended with nylon 6, nylon 666, or nylon 612, asindicated in Table III. For Comparative Examples C7-C9, EVOH wasevaluated alone. For Comparative Example C10, the amorphous polyamideAPA2 was evaluated alone. The weight ratios of the EVOH and thepolyamide in each blend is indicated in Table III. Blending andextrusion were accomplished in the same manner as in Example 1, exceptthat the blending speed was 150 rpm.

Physical Properties of Films

Films, 0.01 to 0.05 mm thick, were cast from the above blends and, forcomparison, from unblended EVOH resins, as indicated in Table III. Thefilms were cast on a coextrusion casting line, with polypropylene layersapproximately 0.25 mm thickness on each side of the sample film extrudedsimultaneously. These polypropylene layers were separated and discardedbefore testing of the film samples. The purpose of this procedure was tosimulate a thin core barrier layer produced during coextrusion. Theoxygen permeabilities of these film samples were measured as for Example1, and are presented in Table III. It may be seen that the oxygenpermeabilities of films prepared from blends of amorphous polyamides andEVOH are significantly better than those of the corresponding blends ofEVOH and nylon 6 or nylon 666 copolymer.

The pin hole flex lives (ASTM F-456) of the films of these examples andcomparative examples were measured, and are reported in Table III. Pinhole flex life is an important measure of film toughness, since theformation of pin holes in a barrier film due to flexing results indegradation of barrier properties. Surprisingly, the pin hole flex livesof the films prepared from EVOH and APA2 blends are better than those ofthe comparative examples prepared from the unmixed blend components(C7-C10).

Preparation and Thermoforming of Multilayer Structures

Multilayer sheet samples were prepared using the materials of Examples2-6 and Comparative Examples C4-C7 and C9, using the same procedure aswas used with Example 1, except that the cooling water used was 70° C.Subsequently these multilayer samples were thermoformed using the sameconditions as for Example 1, and were analyzed for discontinuities inthe walls in the same manner as in the earlier examples. The results areshown in Table IV. It is clear that the containers made from the blendsof the present invention are superior to those made using either EVOHalone as a core material, or to those made using blends of EVOH withcrystalline nylon as the core material.

                  TABLE III.sup.1                                                 ______________________________________                                        EXAM-  POLY-           THICKNESS       PINHOLE                                PLE    AMIDE    (%)    (mm)      OPV.sup.2                                                                           FLEX.sup.3                             ______________________________________                                        2      APA2     10     0.048     0.0039                                                                              1500                                   3      APA2     20     0.040     0.0031                                                                              1410                                   4      APA2     20     0.015     0.0047                                                                              1759                                   5      APA2     30     0.017     0.0050                                                                              1585                                   6      APA2.sup.4                                                                             20     0.012     0.0023                                                                              1750                                   C4     nylon 6  20     0.014     0.0194                                                                              2855                                   C5     nylon 666                                                                              20     0.026     0.0174                                                                              2698                                   C6     nylon 612                                                                              20     0.018     0.0012                                                                              1998                                   C7     none      0     0.045     0.0047                                                                               892                                   C8     none      0     0.023     0.0031                                                                              1270                                   C9     none      0     0.020     0.0019                                                                              1150                                   C10    APA2     100    0.018     --    1092                                   ______________________________________                                         .sup.1 A dash (--) indicates that the measurement was not made.               .sup.2 OPV defined as in Table I.                                             .sup.3 cycles to failure                                                      .sup.4 containing 10% glycerol                                           

                  TABLE IV                                                        ______________________________________                                        THERMOFORMED COEXTRUDED SHEET                                                          TEMP             BREAKS/ NECKDOWNS/                                  EXAMPLE  (°C.)                                                                          DRAW     25 mm   25 mm                                       ______________________________________                                        2        159     7.0      1       18                                          3        159     7.1      1        7                                          4        161     7.1      0        0                                          5        159     6.4      0        0                                          6        159     6.8      0        1                                          C4       159     7.4      9       37                                          C5       157     6.3      9       45                                          C6       159     7.2      17      38                                          C7       156     8.2      12      31                                          C9       160     6.2      34       7                                          ______________________________________                                    

Examples 7-8 and Comparative Examples C11-C13 Preparation of Blends

The EVOH polymer of Example 1 was melt blended with a variety ofpolyamides, as indicated in Table V. For these examples mixtures of theamorphous polyamide APA2, defined above, and a crystalline polyamide,nylon 6 (polycaprolactam) were blended with the EVOH. The polyamidemixtures were prepared by melt blending the two polyamides in a batchextruder at 250° C., before further blending with EVOH at 225° C. in a30 mm twin screw extruder. In comparative Examples C11-C13, EVPH wasblended with nylon 6 alone (C13), or was used without addition of anypolyamide (C11, C12). The EVOH used in C11 and C13 was the same as thatof Example 1; that of C12 contained 44 mol % ethylene and had a meltindex of 16. After blending on the twin screw extruded, the blend wasextruded and pelletized as in Example 1.

Physical Properties of Films

Table V lists the barrier properties of monolayer films prepared fromthe above blends or unblended EVOH resins, prepared and measured as inExample 1. The oxygen barrier properties of the blend of EVOH with themixture of amorphous and crystalline polyamide are comparable to thoseof unblended EVOH.

Preparation and Orientation of Multilayer Structures

The blends and unblended EVOH resins were coextruded into multilayerstructures substantially as in Example 1. The adhesive layers, eachabout 0.01 to 0.03 mm thick, were a maleic anhydride grafted copolymerof propylene and ethylene with a melt index of 7. The temperature of theextruder for the adhesive layers was maintained at 230° C., the extruderfor the core layer at 225° C., the cooling water at 70° C., and thecasting speed was about 4 m/min The thicknesses of the multilayer filmsare reported in Table VI.

Thereafter the multilayer structures were biaxially oriented with a filmstretcher (manufactured by T. M. Long Co.) under the conditionsindicated in Table VI. The drawing was simultaneously in the machine andtransverse directions, at 4000% per minute. The oxygen transmission rateand film quality of the oriented films are listed in Table VI. Haze wasmeasured according to ASTM D-1003.

The results in Table VI show that the multilayer structures of Examples7 and 8 had excellent drawability, and the resulting oriented filmsexhibited excellent oxygen barrier and optical properties. In contrast,the structures of Comparative Examples C11 and C12 cannot withstand thedrawing operation. Under optical microscopy, discontinuity (breakdown)in the core layer is observed. The addition of 20% nylon 6 in C13improved the drawability somewhat, but the results were stillunsatisfactory. Optical microscopy showed that the core layer was drawnunevenly (neckdown). Both breakdown and neckdown had a noticeable effecton the appearance of the oriented film.

                                      TABLE V                                     __________________________________________________________________________                             FILM                                                          POLYAMIDES      THICK                                                EX % EVOH                                                                              AMORPH., %                                                                            CRYSTAL., %                                                                           (mm) OPV                                                                              (% RH)                                       __________________________________________________________________________    7  80    16      4       0.066                                                                              0.067                                                                            (79)                                         8  80    12      8       0.047                                                                              0.082                                                                            (79)                                         C11                                                                              100   0       0       0.025                                                                              0.070                                                                            (80)                                         C12                                                                              100   0       0       0.025                                                                              0.296                                                                            (80)                                         C13                                                                              80    0       20      0.035                                                                              0.141                                                                            (76)                                         __________________________________________________________________________

                                      TABLE VI                                    __________________________________________________________________________            STRETCH                                                                       CONDIT'N                                                                             ORIENTED        HAZE                                           EX THICK..sup.1                                                                       RATIO, °C.                                                                    THICK, mm                                                                            OTR.sup.2                                                                         (% RH)                                                                             (%) QUAL.sup.3                                 __________________________________________________________________________    7  .071/.73                                                                           4 × 4 145                                                                      0.019  20.8                                                                              (89) 2.0 A                                                  6 × 6 150                                                                      0.016  30.5                                                                              (90) --  B                                          8  .069/.72                                                                           4 × 4 145                                                                      0.019  23.4                                                                              (89) 2.0 A                                                  6 × 6 155                                                                      0.014  17.1                                                                              (80) 1.7 A                                          C11                                                                              .061/.72                                                                           4 × 4 145                                                                      0.025  1300                                                                              (80) --  D                                                  6 × 6 155                                                                      0.015  2300                                                                              (80) --  D                                          C12                                                                              .053/.72                                                                           4 × 4 145                                                                      0.023  2200                                                                              (80) --  D                                                  6 × 6 155                                                                      --     --       --  D                                          C13                                                                              .071/.72                                                                           4 × 4 145                                                                      0.042  89.3                                                                              (80) 2.6 C                                                  6 × 6 155                                                                      0.014   215                                                                              (80) 1.5 C                                          __________________________________________________________________________     .sup.1 Thickness of core layer/thickness of total multilayer structure        before stretch, in mm.                                                        .sup.2 Oxygen Transmission Rate in cc/m.sup.2 -24 hratm at 30° C.      and the relative humidity indicated.                                          .sup.3 Quality of film: A  excellent; B  slight haze; C  neckdown; D          breakdown.                                                               

Examples 9-10 and Comparative Examples C14-C17 Preparation of Blends

the same EVOH was used as in Example 1, except for Comparative ExampleC14, which used the EVOH of C12. EVOH and polyamides were blendedtogether as in Example 7. The amorphous polyamide was APA2; thesemicrystalline nylons of each blend were as indicated in Table VII. Thebarrier properties of these monolayer films are presented in Table VII.

Preparation and Orientation of Multilayer Structures

Five-layer coextruded sheets were prepared as in Example 7, except thatthe adhesive resin had a melt index of 2, and the surface structurallayers were propylene/ethylene copolymers with a melt flow index of 2and a density of 0.90. These multilayer structures were biaxiallyoriented as in Example 7. The barrier properties and film quality of theoriented films are reported in Table VIII.

The results show that the multilayer structures of Examples 9 and 10only could be satisfactorily oriented. Those oriented films hadexcellent optical and barrier properties and were heat shrinkable, asindicated in Table IX. Modulus, tensile strength, and elongation weremeasured according to ASTM D882. Film shrinkage was obtained byimmersing the oriented film in oil at 120° C to measure the percentshrinkage of film length. Shrink force was measured according to ASTM2838. None of the comparative examples was satisfactory. C14 wasdifficult to draw and the resulting oriented film was very hazy. BothC15 and C17 could not withstand the drawing conditions. The orientedfilm of C16 exhibited neckdown.

                                      TABLE VII                                   __________________________________________________________________________                             FILM                                                          POLYAMIDES      THICK                                                EX % EVOH                                                                              AMORPH., %                                                                            CRYSTAL.sup.1, %                                                                      (mm) OPV                                                                              (% RH)                                       __________________________________________________________________________     9 80    12      A,   8  0.047                                                                              0.082                                                                            (79)                                         10 80    12      B,   8  0.048                                                                              0.107                                                                            (79)                                         C14                                                                              80    20           0  0.051                                                                              0.110                                                                            (80)                                         C15                                                                              80    20           0  0.051                                                                              0.268                                                                            (76)                                         C16                                                                              80     0      B,  20  0.038                                                                              0.143                                                                            (76)                                         C17                                                                              92     0      A,   8  --   --                                              __________________________________________________________________________     .sup.1 Semicrystalline polyamide A is nylon 6; B is a copolymer of 85         parts nylon 6 and 15 parts nylon 66, melting point 202° C.        

                                      TABLE VIII                                  __________________________________________________________________________            STRETCH                                                                       CONDIT'N                                                                             ORIENTED         HAZE                                          EX.                                                                              THICK..sup.1                                                                       RATIO, °C.                                                                    THICK, mm                                                                            OTR.sup.2                                                                          (% RH)                                                                             (%) QUAL.sup.3                                __________________________________________________________________________    9  .041/.56                                                                           6 × 6, 130                                                                     0.018  17.1 (80) 1.5 A                                                 6 × 6, 140                                                                     0.014  19.5 (80) 1.4 A                                         10 .061/.63                                                                           6 × 6, 130                                                                     --     --            F                                                 6 × 6, 140                                                                     0.014  15.5 (80) 1.2 A                                         C14                                                                              .053/.64                                                                           6 × 6, 130                                                                     0.019  10.7 (80) 9.7 H                                                 6 × 6, 140                                                                     0.014  >3000                                                                              (80) 18.3                                                                              D                                         C15                                                                              .051/.59                                                                           6 × 6, 130                                                                     0.015  1500 (80) 34.7                                                                              D                                                 6 × 6, 140                                                                     --     --        7.6 D                                         C16                                                                              .056/.58                                                                           6 × 6, 130                                                                     --     --        --  F                                                 6 × 6, 140                                                                     0.013  33.5 (79) 1.3 G                                         C17                                                                              .061/.66                                                                           6 × 6, 130                                                                     --     --        --  F                                                 6 × 6, 140                                                                     --     --        5.8 D                                         __________________________________________________________________________     .sup.1 Thickness of core layer/thickness of total multilayer structure        before stretch, in mm.                                                        .sup.2 Oxygen Transmission Rate in cc/m.sup.2 -24 hratm at 30° C.      and the relative humidity indicated.                                          .sup.3 Quality of film: A excellent; D breakdown; F failed to draw; G         good; H hazy, difficult to draw.                                         

                                      TABLE IX                                    __________________________________________________________________________    MULTILAYER FILMS                                                                  Modulus                                                                            Tensile                                                                             Elong.                                                                             Shrink..sup.1                                                                      Shrink force                                         Ex. (MPa)                                                                              Str (MPa)                                                                           (%)  (%)  (MPa, 120° C.)                                                                 OTR.sup.2                                    __________________________________________________________________________    9   1930 165    91  20   3.51    15.3                                         10  1830 159   104  19   3.10    16.7                                         __________________________________________________________________________     .sup.1 Shrinkage and shrink force measured on films obtained by stretchin     5X in each direction at 135° C.                                        .sup.2 Oxygen transmission rate as in Table VIII.                        

Example 11

A blend was prepared as in Example 8, and a five-layer structure wasprepared as in Example 7, except that the adhesive was a maleicanhydride grafted linear low density polyethylene with a melt index of3.5 (ASTM D-1238), and the structural material was a linear low densitypolyethylene. The total thickness of the structure was 0.67 mm; thethickness of the core layer was 0.04 mm. When this multilayer structurewas stretched 4× in each direction at 110° C., a slightly hazy film(Haze =6.7%), 0.30 mm thick, was obtained. The same stretching at 120°C. resulted in a slightly hazy film (Haze =8.1%) 0.028 mm thick. Whenstretching 6× in each direction at 110° C. was attempted, the filmfailed to draw.

Examples 12-19 Preparation of Blends

The same EVOH and amorphous polyamide were used as in Example 7. Threetypes of semicrystalline nylon were used, as indicated in Table X. ForExamples 12-18 the blending was performed as in Example 7. For Example19, the three components of the blend were blended at 230° C. in onestep on a 30 mm twin screw extruder. Table X reports the barrierproperties of monolayer films prepared from these blends.

Preparation and Orientation of Multilayer Structures

Five-layer coextruded sheets were prepared using the materials ofExamples 12-19 as the core layer, using the procedure of Example 7. Theouter structural polymer was a propylene homopolymer, melt index 6. Theadhesive polymer was that of Example 9. These multilayer sheets werebiaxially oriented as in Example 7. All the oriented film exhibitexcellent barrier properties and optical appearance as indicated inTable XI.

                                      TABLE X                                     __________________________________________________________________________                              FILM                                                          POLYAMIDES      THICK OPV                                           EX. % EVOH                                                                              AMORPH., %                                                                            CRYSTAL.sup.1, %                                                                      (mm)  (79% RH)                                      __________________________________________________________________________    12  90     8      A,   2  --    --                                            13  70    24      A,   6  0.044 0.102                                         14  60    32      A,   8  0.036 0.133                                         15  80    14      A,   6  0.061 0.130                                         16  80     8      A,  12  0.065 0.126                                         17  65    21      A,  14  0.042 0.122                                         18  80    12      B,   8  0.048 0.087                                         19  80    14      C,   6  0.036 0.082                                         __________________________________________________________________________     .sup.1 Semicrystalline polyamide A is nylon 6; B is a copolymer of 85         parts nylon 6 and 15 parts nylon 66, melting point 202° C.; C is a     copolymer of 27 parts nylon 6 and 73 parts nylon 66, m.p. 216° C. 

                                      TABLE XI.sup.1                              __________________________________________________________________________               STRETCH                                                                       CONDIT'N                                                                             ORIENTED        HAZE                                        EX.                                                                              THICKNESS                                                                             RATIO, °C.                                                                    THICK, mm                                                                            OTR (% RH)                                                                             (%)                                         __________________________________________________________________________    12 .119/.62                                                                              6 × 6, 145                                                                     0.015  11.9                                                                              (91) 3.6                                         13 .053/.56                                                                              7 × 7, 145                                                                     0.009  40.1                                                                              (91) 2.2                                         14 .053/.56                                                                              7 × 7, 145                                                                     0.009  71.1                                                                              (91) 2.1                                         15 .051/.56                                                                              6 × 6, 145                                                                     0.015  57.4                                                                              (92) 2.1                                         16 .051/.56                                                                              6 × 6, 145                                                                     0.013  58.6                                                                              (92) 1.5                                         17 .051/.56                                                                              6 × 6, 145                                                                     0.013  66.7                                                                              (92) 1.5                                         18 .053/.56                                                                              7 × 7, 145                                                                     0.010  66.7                                                                              (92) 1.4                                         19 .053/.56                                                                              6 × 6, 145                                                                     0.013  31.9                                                                              (92) 2.3                                         __________________________________________________________________________     .sup.1 Terms as defined in Table VI.                                     

Example 20 and Comparative Examples C18-C19

The blend of Example 20 was the same as that of Example 7. The blends ofComparative Examples C18 and C19 are the same as those of ComparativeExamples C11 and C12, respectively.

Five-layer coextruded sheet samples were prepared using the materials ofExample 20, C18, and C19 as the core layer, styrene homopolymer with amelt flow index of 1.3 (ASTM D-1238 condition G) as the two outerlayers, and a maleic anhydride grafted copolymer of ethylene and vinylacetate with a melt flow index of 3 as the two adhesive layers. Thesheet was prepared as in Example 7. The total thickness of each sheetwas about 1.3 mm and the core layer thickness was about 0.10-0.13 mm.

Subsequently the sheets were thermoformed by solid state pressureforming on a thermoformer into cylindrical, cup-shaped containers, 65 mmdiameter at top and bottom and 65 mm deep. The sheet samples were heatedby a ceramic heater operating at 320 to 380° C. The sheet samplesattained the temperatures indicated in Table XII. Forming wasaccomplished using plug assist, air pressure of 480 kPa, and moldingrates of 10 to 12 cycles per minute.

Microscopic examination of the cross section of the container sidewallscut perpendicular to the axis revealed breakdown or neckdown of the EVOHcores for Comparative Examples C18 and C19. It is believed that theseare the result of exceeding the formability limits of these EVOH resinsduring the thermoforming operation. Even the EVOH with 44 mol % ethylenecannot avoid this limitation at the temperatures indicated in Table XII.In contrast the containers made from Example 20 did not exhibit corediscontinuity. To quantify these findings, counts were made of the coreinterruptions (discontinuities or breaks) and core neck-downs (thinningof the core layer without actual discontinuity) per 25 mm (1 inch) wallsection. The results in Table XII show the superiority of the structuresprepared from the blend of the present invention. Discontinuitiesnecessarily result in loss of barrier performance.

                  TABLE XII                                                       ______________________________________                                        THERMOFORMED COEXTRUDED SHEET                                                        Forming Temp.  Breaks/  Neckdowns/                                     Ex.    (°C.)   25 mm    25 mm                                          ______________________________________                                        20     110            0         3                                                    120            0         2                                                    130            0         0                                             C18    110            2        25                                                    120            1        25                                                    130            0        20                                             C19    110            1        25                                                    120            2        24                                                    130            0        12                                             ______________________________________                                    

Example 21 and Comparative Examples C20-C22

The blend of Example 21 was the same as that of Example 8. C20 was thesame EVOH used in preparing Example 8. C21 was the same blend as C16.C22 was the same blend as C17. Table XIII lists the melt flow rate (meltindex) of these examples and comparative examples (ASTM D-1238) measuredafter exposure to 230° C. in the melt index barrel for various timeintervals. The melt flow index of Comparative Examples C21 and C22decreased significantly with increased holding time. Example 21exhibited much more stable melt flow.

                  TABLE XIII                                                      ______________________________________                                        MELT STABILITY                                                                Melt Flow, g/10 min.                                                          Ex.     5 min.        60 min. 90 min.                                         ______________________________________                                        21      4.7           2.50    1.70                                            C20     5.9           3.40    2.30                                            C21     4.9           0.25    0.08                                            C21     4.8           1.10    0.23                                            ______________________________________                                    

Thermal stability of EVOH resin is important for successful meltprocessing. Blending semicrystalline nylon into EVOH is known to causean increase in melt viscosity. It is believed that chemical reactionoccurs between the nylon and the EVOH. It is surprising that the EVOHblends of this invention have a much more stable viscosity.

We claim:
 1. A multiple layer structure wherein at least one of thelayers is prepared from a blend consisting essentially of about 50 toabout 95 percent by weight of an ethylene vinyl alcohol copolymer havinga copolymerized ethylene content of about 20 to about 60 mole percentand a degree of saponification of at least about 90 %, and about 5 toabout 50 percent by weight of a polyamide blend consisting essentiallyof about 30 to about 90 percent by weight of at least one amorphouspolyamide characterized by the lack of an endotherm crystalline meltingpeak as measured by differential scanning calorimetry and furthercharacterized by a glass transition temperature of up to about 160° C.,and about 10 to about 70 percent by weight of at least onesemicrystalline polyamide which si miscible with the ethylene vinylalcohol copolymer, said miscibility evidenced by the presence of asingle glass transition temperature or a depressed melting point inblends of such semicrystalline polyamide with said ethylene vinylalcohol copolymer, as measured by differential scanning calorimetry. 2.The multiple layer structure of claim 1 wherein the amorphous polyamidecomprises about 60 to about 80 percent by weight of the polyamide blend.3. The multiple layer structure of claim 1 wherein the ethylene vinylalcohol copolymer is present at about 75 to about 85 percent by weightand the polyamide blend is present at about 15 to about 25 percent byWeight.
 4. The multiple layer structure of claim 1 wherein the amorphouspolyamide is selected from the group consisting of hexamethylenediamineisophthalamide, hexamethylenediamine isophthalamide/terephthalamideterpolymer, having isophthalic/terephthalic moiety ratios of 100/0 to60/40, mixtures of of 2,2,4and 2,4,4-trimethylhexamethylenediamineterephthalamide, copolymers of hexamethylenediamine and2-methylpentamethylenediamine with iso- or terephthalic acids, ormixtures of these acids.
 5. The multiple layer structure of claim 1wherein at least one of the layers comprises a polymer suitable toprovide structural support for the layer of ethylene vinyl alcoholcopolymer and polyamide.
 6. The multiple layer structure of claim 5wherein the polymer providing structural support is selected from thegroup consisting of polybutylene, polypropylene, polypropylenecopolymers with ethylene, polyethylene, polyethylene copolymers,copolymers of ethylene with vinyl acetate, copolymers of ethylene withcarboxylic acids wherein the carboxylic acid is unneutralized or isneutralized to form an ionomer, polyethylene terephthalate, polymersbased on vinyl chloride, polymers based on styrene, and blends of suchpolymers.
 7. The multiple layer structure of claim 4 which also containsat least one layer of adhesive.
 8. A formed structure prepared bysubjecting the multiple layer structure of claim 5 to athree-dimensional deformation process.
 9. The formed structure of claim8 in the form of a container.
 10. A formed structure prepared bysubjecting to a three-dimensional deformation process a multiple layerstructure wherein at least one of the layers is a blend consistingessentially of about 50 to about 95 percent by weight of an ethylenevinyl alcohol copolymer having a copolymerized ethylene content of about20 to about 60 mole percent and a degree of saponification of at leastabout 90%, and about 5 to about 50 percent by weight of an amorphouspolyamide characterized by the lack of an endotherm crystalline meltingpeak as measured by differential scanning calorimetry and furthercharacterized by a glass transition temperature of up to about 160° C.,and wherein at least one of the layers comprises a polymer suitable toprovide structural support for the layer of ethylene vinyl alcoholcopolymer and polyamide.
 11. The formed structure of claim 10 whereinthe blend consists essentially of about 70 to about 90 percent by weightof the ethylene vinyl alcohol copolymer and about 10 to about 30 percentby weight of the amorphous polyamide.
 12. The formed structure of claim10 wherein the multiple layer structure before thermoforming has a totalthickness of about 0.5 to about 3.5 mm.
 13. The formed structure ofclaim 10 wherein the amorphous polyamide has a glass transitiontemperature of about 80° to about 130° C.
 14. The formed structure ofclaim 10 wherein the amorphous polyamide is selected from the groupconsisting of hexamethylenediamine isophthalamide, hexamethylenediamineisophthalamide/terephthalamide terpolymer having isophthalic/terephthalic moiety ratios of 100/0 to 60/40, mixtures of 2,2,4-and2,4,4-trimethylhexamethylenediamine terephthalamide, copolymers ofhexamethylenediamine and 2-methylpentamethylenediamine with iso- orterephthalic acids, or mixtures of these acids.
 15. The formed structureof claim 10 in the form of a container.
 16. The formed structure ofclaim 12 in the form of a container.
 17. The formed structure of claim14 in the form of a container.
 18. The multiple layer structure of claim1 in the form of a biaxially oriented film.
 19. The multiple layerstructure of claim 1 in the form of an oriented shrink film.
 20. Aformed structure prepared by subjecting to a three-dimensionaldeformation process a multiple layer structure wherein at least one ofthe layers is prepared from a blend consisting essentially of about 50to about 95 percent by weight of an ethylene vinyl alcohol copolymerhaving a copolymerized ethylene content of about 20 to about 60 molepercent and a degree of saponification of at least about 90%, and about5 to about 50 percent by weight of a polyamide component consistingessentially of about 30 to 100 percent by weight of at least oneamorphous polyamide characterized by the lack of an endothermcrystalline melting peak as measured by differential scanningcalorimetry and further characterized by a glass transition temperatureof up to about 160° C., and 0 to about 70 percent by weight of at leastone semicrystalline polyamide which is miscible with the ethylene vinylalcohol copolymer, said miscibility evidenced by the presence of asingle glass transition temperature or a depressed melting point inblends of such semicrystalline polyamide with said ethylene vinylalcohol copolymer, as measured by differential scanning calorimetry, andwherein at least one of the layers comprises a polymer suitable toprovide structural support for the layer of ethylene vinyl alcoholcopolymer and polyamide.